The present invention relates to a method for controlling a CNC machine tool, which has cyclically recurring sequences, according to the preamble of patent claim 1 as well as to a control system for a CNC machine, according to the preamble of patent claim 6.
Under control systems one understands the combination of mechanics, electronics and information technology, which in automatisation technology permits a working procedure to automatically take its course according to a predetermined program.
Todays state of such control systems is for example described in the textbook of Manfred Weck, xe2x80x9cWerkzeugmaschinen, Fertigungssystemexe2x80x9d, Volume 3.1, VDI publishing house Duesseldorf, 1995 as well as in Dubbel, xe2x80x9cTaschenbuch fxc3xcr den Maschinenbauxe2x80x9d, 17th edition, Springer publishing house, Berlin 1995.
Generally the control system today is subdivided into three levels or units:
a data input and visualisation unit, also called a man-machine interface (MMI) which permits or makes available the machine and operating data acquisition, the choice of the machine mode to be carried out, the order administration and the process visualisation,
an adaption control unit acting as a central control unit, also called a SPS or PLC (programmable logic controller), with a control program which according to the state of the art obtains the entirety of directions and agreements for the signal processing,
an NC control unit (NC=numeric control), in which function sequences in NC control programs are stored. These NC control programs contain geometric data concerning the path information, technological data such as cutting speed, advance, spindle rotational speed, as well as alter commands, such as tool exchange, the equipping and removal of parts. Recurring movement sequences are filed several times in the NC program in accordance with the recurrence.
Data inputted via the MMI unit for defining the subject to be manufactured are decoded in the NC control unit and are processed further separately according to geometric, technological data and switch commands. Switch commands are transmitted further to the SPS control unit, where they are linked to feedbacks of the machine tool and in accordance with the control program processed step by step, are converted into control commands which synchronise the membered NC program. Geometric and technological data, after the calling-up by way of the NC control unit, produce corresponding axes movement commands for the machine. NC units and SPS units for the puprose of process visualisation inform the actual machine status to the MMI unit.
An important demand of such control systems is that they must be as flexible as possible, so that changes in the mechanics of the CNC machine or in the input mask of the MMI do not require a complete new programming of the machine.
In order to permit an extension of the mechanics of the machine tool, thus the control system disclosed in EP-A-0 553 621 from the start has at its disposal at least two SPS modules, wherein the first SPS module assumes the machine control and the second SPS module is present as a reserve. In the case of a machine extension only the second SPS module needs to be provided with the new machine functions for the further machine movements which are coupled automatically to the first SPS module by the control system. A renewed programming or a replacement of the already present, programmed first SPS module is not necessary.
In EP-A-0 642 066 there is set the object of flexibilising the dialogue guidance, so that the man-machine interface (MMI) may be adapted to the amended requirements of the user in a simple way and manner. A dialogue-orientated programming system for producing control programs has at its disposal a data forwards-backwards access unit which separates each program set up in a programming system into the part control data xe2x80x9cmachine control dataxe2x80x9d and xe2x80x9cdialogue control dataxe2x80x9d which are provided with linkage keys. The machine control data are deposited into a machine program memory and the dialogue control data into a background memory. Via the logic keys they may again be constituted into a control program and filed in the background memory.
The control systems of CNC machines according to the state of the art are generally designed to be able to control as many as possible and as varied as possible machine movements, so that they attempt to form the indeed rigid central control unit more flexible with their SPS modules. This however leads to complex control systems, which as previously may only be changed by qualified specialists.
There are however also machine tools which have a noticable cyclic characteristic. One example of such a type of machine tool is a gearwheel grinding machine. The movements which a machine with a cycled characteristic are to carry out are repeated cyclically. Furthermore for all subjects the same subject shapes are used. The differences in the control system which lead to differently shaped subjects lie only in the operating parameters or control data, not in the basic movement sequences which are defined by individual machining functions. Furthermore the sequences and the hierarchies of the individual machining functions are unambiguously fixed and do not change. The machining functions for themselves as well as their hierarchy amongst one another even with an extension or modification of the machine always remain the same, so that the SPS module of the central control unit accordingly must always transmit the same control commands to the CNC level.
It is the object of the present invention to provide a method for the control of such a CNC machine with a noticeable cyclic characteristic, in particular of a gearwheel grinding machine, as well as to provide a control system, which permit a simple changing of programs and by way of this a high flexibilisation.
This object is achieved by a method with the features of the patent claim 1 as well as a control system with the features of patent claim 6.
The invention is based in the recognition that with machines with cyclically recurring sequences the function control of the machine within the sequence does not change and thus the master-slave principle may be used. By way of this the hierarchies between the central control unit and the NC control unit may be fixed more unambiguously than with the known CNC control systems.
According to the invention the NC program consists of several part programs or function modules which contain individual machining functions and which in each case are provided with an automatically executed hold command. The individual function modules may be called up by way of control codes of the machine control unit, wherein independently of their hierarchical position in the NC program one may change from one function module into the next. The control codes are set by the MMI unit in a context-sensitive manner.
According to the invention data inputted via the MMI unit is separated into function data for the machining functions and into control data for the choice of the function modules, wherein the former is transfered to the NC control unit where in accordance with the NC control unit it is used in this. The control data is transfered to the machine control unit where in the form of control codes or target codes in a central control program they serve the selection of the function modules of the NC program.
This machine control unit replaces the known SPS control unit, since it assumes all exercises of the known SPS control unit. It is furthermore in the position of determining which function module should be run through next and thus assumes to a greater extent the effective control of the CNC machine. With this it fixes the path to be gone through within the program tree from the last activated function module to the new destination of the NC program, wherein the NC program may be run through in any direction. Thus not only does a hierarchical processing take place but also cycles interconnected within each other, a change to equal levels or jumping back to hierarchal higher planes are possible thanks to the machine control unit which by way of transition functions contained in the NC program, the physical preparation of the machine for carrying out the next machining function is ensured.
Since the individual function modules during a single sequence of the NC program may be called up several times, each processing function only needs to be carried out once in the NC program. The NC program according to the invention is thus simply constructed and does not unnecessarily require memory space.
According to the invention the function modules or menu points of an NC program are grouped together to a program tree. Which branch of the program tree is run through is determined by the machine control unit. Since it knows the linkage structure in the program tree it is furthermore in the position of determining the path from one branch to the next. Generally a single NC program is sufficient, the integration of several NC programs in a single NC control unit is however possible.
Thanks to the cooperation, according to the invention, of the MMI unit, the machine control unit and the NC unit, an existing control system may be changed or supplemented in a simple way and manner. If new machining functions are to be introduced, the integration of a new function module in the program tree as well as the placing of a new control code in the MMI unit are sufficient, these being transmitted to the machine control unit. If existing machining functions are to be provided with new control data then their placing in the MMI unit is sufficient. The user may thus carry out supplements and changes without having to change the central control program of the machine control unit. Examples for this are, a change of the data necessary for carrying out the machining procedures, the addition of new data, for example for a new machining tool or for a gearwheel with new dimensions or for carrying out new axis movements. With the changing or supplementing of the control thus not all of the interrelationships must be recognised since the tree structure of the NC program avoids false movements of the machine tool. The use of two primary files which may be copied in any manner, one for the control data and another for the function data, permit a quick and reliable addition of new control elements. Above all in the region of the MMI unit the change may be carried out without compiling by way of pure ASCII editing procedures.
Furthermore the MMI unit, in particular an operation and selection surface may be formed flexible and be changed in a simple way and manner without having to entail a change of the machine control unit.
Furthermore it is advantageous that by way of the control, according to the invention, of the NC program the danger of program call-ups leading to undesired interruptions of the subject machining procedure is avoided.